The invention relates to methods for developing offshore oil and gas fields. One of the biggest challenges in the development of oil and gas fields has been the fact that the reservoirs found in the fields can not be observed except through indirect means, which introduce a large amount of conjecture in the assessment of the actual in-place conditions. In deepwater offshore fields, conventional methods used to mitigate risks in the development have proven problematic, forcing a development regime where the investments are much larger and yet have to be made with less information than is traditionally collected prior to decision making.
Investments involved in the development of oil and gas fields are substantial and subject to high levels of risks. The development of an oil and gas field has generally involved significant up-front data gathering, in order to estimate the risks involved in the project, and engineering, in order to better specify the final delivered product and therefore the costs involved. The process for bringing a field into production involves a number of sequential definitional steps.
Although each company has small variations, the steps involved in the typical development processes 10, which are shown in FIG. 1 and include geological exploration of a field 12, appraisal drilling of wells within the field 14, defining the plan for the development of the field 16, executing the plan 18, and operating the field 19. The geological exploration of a field 12 comprises various preliminary geological investigations and sparse 2D seismic work followed by a 3D seismic survey. If a prospect looks promising an exploration well is drilled. During this process, various reservoir models are generated from the seismic and then updated with information checked against the well results.
Once the initial exploration well has been drilled and some quantity of hydrocarbons has been identified, the appraisal drilling phase 14 starts. In this phase, several additional wells are drilled to delineate the reservoir and gain reservoir information. As the wells are drilled, various logging and testing operations can be performed in order to establish reasonable information to put into the reservoir models, which are then used for better understanding of the various important parameters.
Once the reservoir has been appraised, a plan for development of the field is defined 16. The plan may comprise identification as to the number and location of wells to be drilled, what kind of surface facilities, what type of riser systems, and what export means (pipelines, tankers, etc.) will be used. These plans are all based on the reservoir information that is available, which as discussed above, may be incomplete or inaccurate. Once defined, the plan for development is executed 18, which comprises the procurement and construction of equipment and systems needed for the project. Once the necessary equipment is in place, the field can be operated 19.
During the operation of the field 19, conditions within the field may change or may not be exactly what was predicted during the evaluation and planning phases. Because most of the equipment and systems specified for the field were designed and built to operate under a specific set of conditions, any change to these conditions may cause the equipment to operate at less than optimal efficiency.
Although the processes and their associated faults discussed above are generally used for all fields regardless of location or technical complexity, there are a number of additional factors in the high pressure, high temperature, sub salt portion of the deepwater Gulf of Mexico that make these processes particularly problematic. One of these factors is that, in the deepwater Gulf of Mexico, the seismic technologies are significantly less reliable due to the extreme depths of the targets combined with the complications involved in seismic data acquisition through the salt canopy that covers much of the acreage in the deepwater Gulf of Mexico. Deficiencies in the seismic exploration are often made up for by drilling more exploration wells, but this is not an attractive option because the costs and complexity of drilling a well in these deepwater regions are significant.
Thus, the embodiments of the present invention are directed to methods for developing offshore fields that seek to overcome these and other limitations of the prior art.